As a novel display element, an OLED device has image quality comparable with a thin film transistor-liquid crystal display (TFT-LCD), but its production cost is far less than that of the TFT-LCD. The OLED device has become a research hotspot in the past 20 years due to its advantages in flat-panel display such as high brightness, rich colors, being driven by a low-voltage direct current, and a simple manufacture process, and now it has entered mass production.
Generally, the OLED device includes a rigid glass substrate or a flexible polymer substrate, a transparent anode and a metallic cathode deposited on the substrate, and two or more organic light-emitting layers arranged between the transparent anode and the metallic cathode. The organic light-emitting layers usually include a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer and an electron injection layer. The OLED device is very sensitive to oxygen and moisture, and in the case that oxygen and moisture enter the OLED device, such defects as dark spots and pinholes may occur. In addition, electrodes in the OLED device may be oxidized, and an organic material of the OLED display device may react with oxygen and moisture. As a result, a service life of the OLED device may be adversely affected. Hence, an encapsulation technology is one of the keys to achieve the mass production of the OLED device.